The present invention concerns a method in an adjustablecrown roll (variable-crown roll), in which hydraulic loading elements or a series of hydraulic loading elements are used and which are fitted so as to act in a plane of a nip that can be formed between the variable-crown roll and a counter roll thereof. The elements of series are fitted between a central axle of the variable-crown roll and a cylindrical mantle revolving about the axle and preferably controlled by means of radial bearings. The central axle is supported by means of axle journals thereof on deflection bearings or equivalent.
The present invention further concerns a roll device intended for carrying out the method of the invention, the roll device comprising a massive central axle and a roll mantle revolving on the central axle through radial bearings or under equivalent control. A series of glide-shoe loading-piston elements or a corresponding pressure fluid chamber arrangement is fitted in a space between the axle and the roll mantle, by means of which the profile of the nip that can be formed between the variable-crown roll and a counter-roll thereof can be regulated. The glide-shoe piston series or equivalent can be fitted so as to act substantially in a plane of the nip. The stationary axle is supported from outside the roll mantle, by means of deflection bearings or equivalent.
In paper machines, such rolls are commonly used to form a dewatering press nip, a smoothing nip, or a calendering nip with a counter-roll. In these purposes of use, it is important for the distribution of the linear load of the nip, i.e. the profile in the axial direction of the rolls, to be made unvarying or adjustable as desired, e.g., in order to control the moisture profile and/or thickness profile (caliber) of the web in the transverse direction. For this purpose, variable-crown rolls or adjustable-crown rolls (the term "variable-crown roll" will be used to denote all such rolls below) are known in the prior art, by means of which attempts have been made to act upon the distribution of the linear load in a nip.
Several different variable-crown rolls for paper machines are known in the prior art. As a rule, these roll comprise a massive or tubular stationary roll axle and a roll mantle rotatably arranged about the axle. Arrangements of glide shoes and/or a chamber or a series of chambers for pressure fluid are fitted between the axle and the mantle to act upon an inner face of the mantle, so that the axial profile of the mantle at the nip can be aligned or adjusted as desired. As a rule, the nips formed by such rolls such as press nips or calendering nips, are loaded by means of loading forces applied to the axle journals of the variable-crown roll and of its counter-roll.
When variable-crown rolls are used as press rolls, it is necessary to open the nips formed thereby, e.g. for servicing operation such as replacement of press felts. When a variable-crown roll is used as a calender roll, the calendering nips must be opened, e.g. for the threading of the web.
So-called variable-crown rolls without loading arms are also known in the prior art, in which the stroke length of the piston-cylinder elements of the hydraulic loading components has been arranged to be large enough so that it is also sufficient for producing the opening movement and correspondingly the closing movement of the nip, and so that loading arms acting upon the ends of the roll axle and provided with power units or corresponding cylinder devices, are not even needed at all. In such variable-crown rolls without loading arms, the hydraulic loading elements which act upon the inner face of the roll mantle also produce the nip pressure loading per se, in addition to crown variation and nip profiling.
The prior-art variable-crown rolls without loading arms have favorable properties of their own, but they have also involved, e.g., the drawback of it becoming necessary to reduce the dimensions and the rigidity of the stationary central axle of the variable-crown roll, because a certain intermediate space must be provided between the roll mantle and the central axle for the opening movement, in addition to space that is required at the opposite side relative to the hydraulic loading elements for the deflection of the central axle.
In view of the structural and functional properties of a variable-crown roll, it is however of extreme importance that the central axle must be made as rigid as possible, explicitly in the plane of the nip and in the direction of the hydraulic loading elements. In the opposite direction, the rigidity of the central axle is not of as great importance.